wildknight30: If im missing something here, please would someone point it out.
SP have provided a breakdown of your estimated or actual (which?) consumption. Probably supposed to be 12 months but the Primary unit allocation (commonly 4572/900) makes me wonder if its over 13-14 months. Worth checking that as it would make their usage calculation high.
I calculate you need to increase your monthly payment by £18 just to mark time. Then there are the £315 arrears to be recovered in the next 12 months. They have chosen to add it in to the annual energy costs. That's another £26/month to arrive at the same bill in 12 months with a zero balance. So at least a £44 increase. Like you I don't know where the £50 comes from and the breakdown doesn't explain. In fact it should not be a surprise that there is a debit balance after the winter period as long as there is a matching credit balance after the summer period. Except SP are trying to achieve a zero balance (and probably a credit balance) at the close of the winter. Not right IMHO
You're screwed in the sense that you have a debit balance of £315 which possibly will affect your opportunity to switch.
Possibly your offer seems a bit light but good luck.